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have a 1.5 hp Nocchi jet pump on top of a 20 gallon galvanized iron pressure tank (no bladder or diaphragm). Pressure switch is set to cut in at 20psi and cut out at 40 psi. The set up has been working well for a couple of years until a couple of weeks a ago, for no apparent reason, the inlet piping vibrates and hums/thrums as the tank pressure drops. The vibrating and humming stops when the pump cuts in to fill the tank. Some details I noticed in the most recent observations, the tank will pressure up to 40psi and cuts out as set but steadily drops to about 35 psi and holds. When the taps or showers are in use the pressure will drop and as it reaches 30 psi the humming/thrumming/vibrating starts until the pressure reaches the cut in setting of 20 psi and the pump kicks in to fill the tank.
The pump is supplied from a 150gal reservoir to pump water up to two stories, and the reservoir is filled constantly and no blockages observed.
Iíve drained out the tank from the bottom drain plug and refilled with water to no avail. Iíve tried resetting the pressure switch cut/in/out setting down to no avail. Thereí really been no impact to the in house water supply but I am sure I am doing the pump damage with the vibrating and humming.
On a side note, the piping from the reservoir is all pvc with 4 90 degree joints before finally connecting to the pump inlet. These joints are a constant source of leaks and I want to swap them for a single clamped on 1 inch flexible hose form the reservoir to the pump inlet. Is there any reason not to go this route? I did see somewhere on the internet that the flexible hosing as well as too many angles in getting to the pump inlet is not recommended, although no explanation was given.
Thanks for your help...